Tsarnaev said at a news conference Thursday that he planned to leave that day or the next for the U.S. with the hope of seeing his younger son, who is under arrest, and burying his elder son, who was killed. His family, however, indicated later Thursday that the trip could be pushed back because he was not feeling well.

Tsarnaev confirmed on Sunday that he is staying in Chechnya, a province in southern Russia, but did not specify whether he was hospitalized. He is an ethnic Chechen and has relatives in Chechnya, although he and his family spent little time in Chechnya or anywhere else in Russia before moving to the U.S. a decade ago.

He and the suspects' mother, Zubeidat Tsarnaeva, returned to Russia last year and settled in Makhachkala, the capital of neighboring Dagestan, where Tsarnaeva's relatives live.

During the past week, they were both questioned extensively by U.S. investigators who had traveled to Makhachkala from Moscow. They also were besieged by journalists who staked out their home.

Tsarnaev's family said last week that he intended to get to the U.S. by flying from Grozny, the Chechen capital, to Moscow. He and Tsarnaeva left Dagestan on Friday, but their whereabouts were unclear.